1. Field of the Invention
The present invention relates to an optical beam splitting device and a method of controlling optical beam outputs. More particularly, the present invention relates to an optical beam splitting device that divides an optical beam into a plurality of beams and provides them to a plurality of output ports. The present invention further relates to a method of controlling a plurality of optical beam outputs of an optical beam splitting device.
2. Description of the Related Art
Optical communications technologies have been rapidly brought into the fields of local area networks (LANs) and subscriber telecommunication systems these days. To integrate a highly organized network by using fiber optics, there are increasing demands for optical branching devices that provide connection, division, combination, and other functions to distribute optical beams.
Beam splitters, among the optical branching devices, are optical devices that divide an input light signal into a plurality of separate beams and output them through their respective output ports. Besides being designed to provide this basic feature, some beam splitters are equipped with such a control function that shuts off the output or reduces the output power for safety purposes, when one of the output ports gets open-ended. More specifically, when a fiber optic cable is broken or a cable plug has happened to be removed from optical communication equipment, the network connection is interrupted and a maintenance engineer will be called to solve the problem. During the service, he/she is potentially exposed to a hazardous environment where a light beam is emitted from the open end of the broken cable or from the unplugged receptacle on the equipment, and if the direct beam impinged on his/her eye, it could cause an injury to the retina. The above safety function protects his/her eyes from such a hazard.
FIG. 18 is a block diagram of a beam splitter 100 equipped with a conventional beam output control function. This beam splitter 100 divides a single input light beam amplified by an optical amplifier 120 into eight beams to distribute them through their respective output ports A-H. In the case of cable breaks or plug disconnection, some part of the light beam is reflected at a fiber end face that is left open.
Suppose that such a back reflection has happened to the output port A, for instance. A photodiode PD1 receives the reflected light and transduces it to an electrical signal. A detector 101 examines the voltage level of the electrical signal sent from the photodiode PD1, and if the voltage level exceeds a predetermined reference level, the detector 101 will generate a detection signal indicating the presence of a meaningful back reflection. Upon receipt of this detection signal, an optical amplifier controller 111 sends a control signal to the optical amplifier 120 to stop the emission of the amplified beam or reduce its output power level. Note the above operation will be performed by other components shown in FIG. 18, i.e., photodiodes PD2-PD4, detectors 102-104, and optical amplifier controllers 112-114, if they encountered the same problem.
In the conventional beam splitter 100 outlined above, however, the reflected light detected in one port will affect the beam outputs of all the ports. This disrupts all communication services having been provided to the subscribers involved and thus leads to an extensive degradation in the quality of optical communication services.